(1) Field of the Invention
The present invention relates to a portable mobile terminal and a transmission unit, and more particularly to a portable mobile terminal and a transmission unit suitably applicable to communication systems in which a transmission power needs to be variable.
(2) Description of the Related Art
In mobile communication (multiplex radiocommunication) services including portable telephone services, there is a case that a base station needs the same receive power (reception strength) from mobile units (portable mobile terminals) irrespective of the distances from the mobile units. For instance, this requirement is imposed on a CDMA (Code-Division. Multiple Access) system in which a plurality of mobile units (subscribers) share the same frequency band in a manner that each of the mobile units performs a spread (diffusion) spectrum modulation of a transmission signal using a different code.
This is generally referred to as the xe2x80x9cfar and near (distance) problemxe2x80x9d, and in the case of the CDMA system, a transmission signal (that is, an undesired wave) from another mobile unit produces an interference component to some base station (receiver). For instance, if a mobile unit generating an undesired wave exists in a range close to the base station, significant level interference may take place by that undesired wave; hence, there is a need to equalize the signal reception levels from the mobile units in the base station by controlling the transmission powers of the mobile units finely.
For this reason, the mobile unit needs to be designed such that its transmission power is variable in a range as wide as possible and is controllable in multistage (stepwise) fashion (for example, in units of 1 dB to several dB).
One configuration to realize such a function may be, for example, as shown in FIG. 11. That is, as shown in FIG. 11, in a mobile unit, a transmission system (transmission unit) 1xe2x80x2 is included which principally comprises an oscillator 3, a modulator 4, a variable gain type amplifier (variable gain circuit) 5, a frequency converting section (up-converter) 5C, a power amplifier 6, a directional coupler 7, a duplexer (an antenna sharing unit) 8, a transmission/receive antenna 9, a frequency converting section (down-converter) 10A, a received signal strength indicator (RSSI) detector (a direct-current voltage converting section) 12, a controller 13xe2x80x2 containing a memory 14xe2x80x2, a digital/analog (D/A) converter 15 and others. Incidentally reference numeral 2 designates a reception system made generally to share the transmission/receive antenna 9 with the transmission system 1xe2x80x2 through the duplexer 8.
In this configuration, the oscillator 3 is made to generate a carrier signal, while the modulator (modulating section) 4 is, for example, made to perform an orthogonal modulation (QPSK or the like: primary modulation) of a transmission signal (baseband signals I, Q) through the use of the carrier signal from the oscillator 3, before conducting spread modulation (secondary modulation) thereof with a predetermined spread code. The variable gain (gain varying) circuit 5 is designed to be capable of changing the gain of a transmission signal undergoing the modulation in the modulator 4, with its gain being controlled by the controller 13xe2x80x2 in a state where the D/A converter 15 is interposed therebetween.
The up-converter 5C is made such that a mixer 51 mixes a transmission signal [intermediate frequency (IF) signal], whose gain is changed in the gain variable circuit 5, with a signal from an oscillator 52 to frequency-convert (up-convert) the transmission signal into a radio frequency (RF) signal.
The power amplifier 6 is for conducting a linear amplification of a transmission signal (RF signal) from this up-converter 5C. After passing through the directional coupler 7 and the duplexer 8, the transmission signal amplified is transmitted toward a base station (not shown).
The directional coupler 7 is for deriving a portion of the transmission signal (transmission power) amplified linearly in the power amplifier 6, with the transmission signal, (RF signal) taken out being supplied to the down-converter 10A. The down-converter 10A is for frequency-converting (down-converting) the transmission signal (RF signal) taken out by the directional coupler 7 into a signal with an intermediate frequency (IF) in a manner that a mixer 10 mixes this transmission signal with a signal from an oscillator 11, while the RSSI detector 12 is for converting the transmission signal, down-converted by the mixer 10 into a direct-current voltage (RSSI signal) of a value corresponding to its power [that is, the present transmission power in the transmission system 1xe2x80x2 (the present RSSI in the base station)].
Thus, a portion composed of the directional coupler 7, the mixer 10, the oscillator 11 and the RSSI detector 12 functions as a transmission power detecting section 18 to detect (monitor) the transmission power of the transmission signal amplified by the power amplifier 6.
Furthermore, the controller 13xe2x80x2 is for producing a gain control signal to control the gain of the variable gain circuit 5 so that the aforesaid RSSI signal (the present transmission power of the transmission system 1xe2x80x2) assumes a power value corresponding to a transmission power control signal from a base station (external) detected in the reception system 2. For instance, referring to data representative of the mapping (corresponding relationship) of gain control signals (control voltage values) to RSSI signals and Transmission power control signals, stored in the built-in memory 14xe2x80x2 in advance, the corresponding control voltage value is outputted, for example, in the form of digital data of n-bit (n depicts a natural number).
The D/A converter 15 is for converting the control voltage value (n-bit digital data) outputted from the controller 13xe2x80x2 into analog data which in turn, comes in the variable gain circuit 5.
That is, the controller 13xe2x80x2 and the D/A converter 15, together with the transmission power detecting section 18 (the directional coupler 7, the mixer 10, the oscillator 11 and the RSSI detector 12), form a feedback control system 16 to implement the feedback-control of the present transmission power by adjusting the gain of the variable gain circuit 5 so that the present transmission power assumes a power value corresponding to a transmission power control signal from a base station.
In the transmission system 1xe2x80x2 thus constructed, a carrier signal outputted from the oscillator 3 is fed to the modulator 4 where it is orthogonally modulated with the baseband signals I, Q and then spread-modulated. The output of this modulator 4 passes through the variable gain circuit 5 and the up-converter 5C and reaches the power amplifier 6 to undergo the linear amplification, before being transmitted through the transmission/receive antenna 9 toward a base station.
Meanwhile, at this time, in the feedback control system 16, the directional coupler 7 derives the present transmission power while the controller 13xe2x80x2 controls the gain of the variable gain circuit 5 so that that transmission power comes to a power voltage corresponding to a transmission power control signal from a base station, detected in the reception system 2.
However, in the case of such mobile unit (transmission system 1xe2x80x2), in general the stable gain-variable range the variable gain circuit 5 can provide is approximately 30 dB to 40 dB. Accordingly, although operating well when the gain-variable range needed is relatively narrow (for example, the PDC system requires approximately 20 dB), the mobile unit handles poorly when the gain-variable range needed is extremely wide (particularly, the CDMA system requires approximately 70 dB). In addition, extreme difficulty is experienced to realize a single variable gain amplifier providing a stable gain-variable range above approximately 70 dB according to the existing technique.
Moreover, in systems such as the CDMA system requiring fine (multistage) control of the transmission power over a wide range to accompany the xe2x80x9cfar and near problemxe2x80x9d, there is a need to reduce the phase variation (phase varying quantity) of the transmission signal to the gain variation (gain varying quantity) as much as possible (in general, within 5xc2x0/dB). However, depending upon circuit arrangement, the phase variation to the gain variation of one variable gain circuit 5 can reach up to approximately 10xc2x0/dB. This can make it difficult to demodulate signals normally in a base station.
The present invention has been developed in consideration of these problems, and it is therefore an object of this invention to provide a portable mobile terminal and a transmission unit which are capable of controlling the transmission power in multistage fashion over a wide range, and of minimizing the phase variation of the transmission signal at this time.
For this purpose, in accordance with this invention, there is provided a portable mobile terminal comprising a modulating section for modulating a transmission signal by using a spectrum spread system; an amplifying section for amplifying the transmission signal, modulated by the modulating section, to a needed transmission power; a frequency converting section put between the modulating section and the amplifying section for conducting a frequency conversion of the transmission signal, modulated by the modulating section, into a radio-frequency signal; a plurality of variable gain units provided between the modulating section and the amplifying section to be connected in series to each other to be capable of changing the gain of the transmission signal modulated by the modulating section, and respectively having gain-to-phase characteristics set so that a phase variation of the transmission signal caused by the entire gain variation of the variable gain units is cancelable; and a control section for controlling a gain of each of the variable gain units in accordance with a transmission power control signal from a base station.
Thus, with the portable mobile terminal according to this invention, the control section controls the gain of each of the variable gain units in accordance with an instruction from the base station, thereby controlling the transmission power in multistage fashion over a wide range and minimizing the phase variation of the transmission signal at that time without conducting special phase compensating control. Accordingly, it is possible to realize and provide a terminal which can sufficiently satisfy the conditions (wide-range multistage transmission power control and low phase variation) the CDMA system requires.
In this case, although, when all the variable gain units are provided on the output side of the frequency converting section, the more succeeding variable gain units show easier saturation, if some of the variable gain units are provided on the input side of the frequency converting section for frequency-converting a transmission signal into a radio-frequency signal while the remaining variable gain units are installed on the output side of the frequency converting section, such a phenomenon is suppressible.
Furthermore, if as the aforesaid plurality of variable gain units there are provided a first variable gain unit capable of changing the gain of a transmission signal from the modulating section and a second variable gain unit connected in series to the first variable gain unit to enable changing the gain of the transmission signal from the first variable gain unit and having a gain-to-phase characteristic to permit canceling a phase variation of the transmission signal caused by the gain variation of the first variable gain unit, this portable mobile terminal is realizable with an extremely simple configuration.
Also in this instance, although, when all these variable gain units are put on the output side of the frequency converting section, there is a possibility that the succeeding second variable gain unit gets into its saturated condition, if the first variable gain unit is provided on the input side of the frequency converting section while the second variable gain unit is installed on the output side of the frequency converting section (that is, if the frequency converting section is interposed between the first variable gain unit and the second variable gain unit), such a phenomenon is suppressible.
Still further, it is also appropriate that the aforesaid control section is made to be capable of controlling the gain of each of the variable gain units by a control signal common to the variable gain units, or that it is made to be capable of controlling the gains of the variable gain units in a predetermined order by individual control signals for the variable gain units.
With the former, the simplification of the control section is feasible, which contributes greatly to the size reduction of this portable mobile terminal. On the other hand, with the latter, there is no need to control the gains of all the variable gain units simultaneously at the transmission power control, which can improve the signal-to-noise ratio in this portable mobile terminal.
Moreover, in accordance with this invention, there is provided a transmission unit comprising a modulating section for modulating a transmission signal; an amplifying section for amplifying the transmission signal, modulated by the modulating section, to a needed transmission power; a plurality of variable gain units provided between the modulating section and the amplifying section to be connected in series to each other to enable changing a gain of the transmission signal, modulated by the modulating section, and respectively having gain-to-phase characteristics whereby a phase variation of the transmission signal caused by the entire gain variation of the variable gain units is cancelable; and a control section for controlling the gain of each of the variable gain units.
Thus, with the transmission unit according to this invention, the control section controls the gain of each of the variable gain units, thereby controlling the transmission power in multistage fashion throughout a wide range and minimizing the phase variation of the transmission signal without requiring special phase compensating control.
Also in this instance, if as the aforesaid plurality of variable gain units there are provided a first variable gain unit capable of changing the gain of a transmission signal from the modulating section and a second variable gain unit connected in series to the first variable gain unit to enable changing the gain of the transmission signal from the first variable gain unit and having a gain-to-phase characteristic to permit canceling a phase variation of the transmission signal caused by the gain variation of the first variable gain unit, this portable mobile terminal is realizable with an extremely simple configuration.
Furthermore, it is also appropriate that the aforesaid control section is made to be capable of controlling the gain of each of the variable gain units by a control signal common to the variable gain units, or that it is made to be capable of controlling the gains of the variable gain units in a predetermined order by individual control signals for the variable gain units.
Still further, also in this instance, with the former, the simplification of the control section is feasible, which contributes greatly to the size reduction of this portable mobile terminal. On the other hand, with the latter, there is no need to control the gains of all the variable gain units simultaneously at the transmission power control, which can improve the signal-to-noise ratio in this portable mobile terminal.
Besides, if the aforesaid modulating section is designed to modulate a transmission signal according to a spectrum spread system, it is possible to realize a transmission unit sufficiently meeting even the CDMA system particularly requiring the wide-range multistage transmission power control and the low phase variation.